linux-kernel - Re: [RFC PATCH tip 0/5] tracing filters with BPF

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Message-ID: <y0my53zqmy1.fsf@fche.csb>
Date:	Thu, 05 Dec 2013 11:31:18 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Alexei Starovoitov <ast@...mgrid.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	Jovi Zhangwei <jovi.zhangwei@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH tip 0/5] tracing filters with BPF

Andi Kleen <andi@...stfloor.org> writes:

> [...]  While it sounds interesting, I would strongly advise to make
> this capability only available to root. Traditionally lots of
> complex byte code languages which were designed to be "safe" and
> verifiable weren't really. e.g. i managed to crash things with
> "safe" systemtap multiple times. [...]

Note that systemtap has never been a byte code language, that avenue
being considered lkml-futile at the time, but instead pure C.  Its
safety comes from a mix of compiled-in checks (which you can inspect
via "stap -p3") and script-to-C translation checks (which are
self-explanatory).  Its risks come from bugs in the checks (quite
rare), problems in the runtime library (rare), and problems in
underlying kernel facilities (rare or frequent - consider kprobes).


> So the likelyhood of this having some hole somewhere (either in
> the byte code or in some library function) is high.

Very true!


- FChE
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